There is commercially available a printer in which a memory card or the like is mounted and which can read out and print image data stored in the memory card, i.e., a so-called direct printer (see Japanese Patent Laid-Open No. 11-007701). Some direct printers can be used as general PC printers when they each comprise an interface with a host computer. Some can be used as apparatuses which can read/write data from/to memory cards mounted in the apparatuses. Some can be connected to digital cameras through cables or by radio, receive image data stored in the digital camera, and print an image.
The operation unit of such direct printer has a plurality of operation keys to designate print settings or various functions. The user can make various settings such as selection of an image to be printed, designation of the number of printed images, setting of the printing layout, and the like by operating the operation keys of the operation unit. If the printer is provided with a display for image display, it can display images on the display and select an image to be printed. There is also available a direct printer which can perform image editing such as adding a character string to an image to be printed or overlaying another image on the image to be printed using the operation unit.
A general procedure for using such direct printer will be described. Index printing is performed to show a list of all image data stored in a memory card while adding a unique character string such as an image number to each image. An image is selected from ones stored in the memory card and is printed using a number corresponding to the image obtained by the index printing. Direct printers to which an external storage device such as a hard disk can be connected each have a backup function of storing image data from a memory card in the external storage device. Some of these printers can preserve the image data of the memory card using the backup function. The printers can perform index printing of image data preserved in the external storage device and can print an image selected from the preserved image data.
The capacity of a memory card has rapidly been increasing in recent years, and the capacity of a memory card used in a digital camera has also been increasing. Along with an increase in memory card capacity, the entire capacity of each memory card is not consumed during one trip or the like. The same memory card can be used in photographing another event or the like without deleting photographed images in the memory card. In this case, image data photographed by a digital camera and stored in the memory card may temporarily be saved in the external storage device connected to the direct printer without deleting the image data in the memory card, and the memory card may be used again. In this case, previously photographed image data remains in the memory card. If the digital camera executes photographing using a free space in the memory card without initializing the memory card, the memory card contains the previously photographed image data in addition to newly photographed image data.
If image data of the memory card is repeatedly saved into the external storage device upon photographing in the above described situation, a plurality of identical image data are stored in the external storage device. If index printing for the image data stored in the external storage device or all image printing in which all images in the external storage device are printed one by one, or two or more at a time is performed, the identical images are printed for the number of the identical images. This wastes printing materials such as a printing sheet, ink, and the like. To specify duplicated images, it is necessary for index printing or all image printing of the image data stored in the external storage device, and a user compares the printed images with each other to determine whether they include identical images. This work is troublesome to the user.